Functional organization of distance-dependent audio-tactile integration is different in rear and front spaces

Peripersonal space mediates animals' interactions with the environment and is thus critical for the implementation of appropriate behaviors. Integrating multisensory information located in peripersonal space induces enhanced behavioral responses and reflects the relevance of external stimuli for the organism's survival. To date, modifications of reaction time related to peripersonal space have mostly been studied using stimuli presented in the frontal space, and limited data are available on other dimensions of peripersonal space. Here, we investigated rear and front defensive peripersonal space by testing whether the distance-dependent behavioral effect of audio-tactile integration varies around the body. Healthy human participants had to detect a tactile stimulation on their hand while an irrelevant sound was approaching them from different parts of space. We used sound spatialization techniques (3D sound) to create sound stimuli looming towards participants' bodies from the front-right, front-left, rear-right, and rear-left quadrants. In the front hemifield, sounds approaching from the left had to be closer to facilitate tactile detection compared to those from the right. In contrast, in the rear hemifield, tactile detection was enhanced at similar distances regardless of whether the sound approached from the left or right. This indicates that human auditory defensive peripersonal space is not homogeneous around the body, showing a lateral asymmetry in the front but not in the rear space. This suggests that perceptual coding of space takes into account action abilities which, in humans, are driven by a front/back organization of the biomechanic skeletal system and of the sensory organs.